During the formation of a semiconductor device, many features such as conductive lines, contacts, dielectric isolation, and other features are commonly formed over and within a semiconductor wafer. A goal of semiconductor device engineers is to form as many of these features in a given area as possible to increase yields, decrease manufacturing costs, and to miniaturize devices. The formation of these structures typically requires the use of lithography. Optical lithography, the lithographic method most used in leading-edge wafer processing, comprises projecting coherent light of a given wavelength, typically 248 nanometers (nm) or 193 nm, from an illumination source (illuminator) through a quartz photomask or reticle having a chrome pattern representative of features to be formed, and imaging that pattern onto a wafer coated with photoresist. The light chemically alters the photoresist and enables the exposed photoresist (if positive resist is used) or the unexposed photoresist (if negative resist is used) to be rinsed away using a developer.
Semiconductor device processing often requires the formation of symmetrical features having uniform sizes, and asymmetrical features having different sizes. To form symmetrical features, a reticle having a regular chrome pattern is used to expose the photoresist. The formation of asymmetrical features, features having two (or more) different shapes and/or electrical properties, typically requires the use of two (or more) reticles, with one reticle defining the pattern of each feature.
The manufacture of reticles is time consuming and expensive due to the complexity of a typical reticle used in semiconductor device fabrication. A photolithography method which provides for the selective formation of either symmetrical features or asymmetrical features using a single reticle would be desirable.
It should be emphasized that the drawings herein may not be to exact scale and are schematic representations. The drawings are not intended to portray the specific parameters, materials, particular uses, or the structural details of the invention, which can be determined by one of skill in the art by examination of the information herein.